<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<style>
			div span {
				color: red;
			}
		</style>
	</head>
	<body>
		<!-- 后代集 -->
		<!-- 将父集中对应关系的子集全部改变 -->
		<span>外部盒子</span>
		<div>
			<span>孙盒子</span>
			<p><span>孙孙盒子</span></p>
		</div>
	</body>
</html>